Ordered and nanostructured materials can provide unique micro- and nano-structures and exceptional size-dependent properties. This class of materials may be tailored to provide materials for novel catalytic, sensors, membranes, structural, electric, magnetic, and biomaterials applications. Nanostructured materials often are used to refer to materials whose structural elements—clusters, crystallites or molecules—have dimensions in the 1 nm to about 100 nm range. Academic and industrial interests in these materials continue to rise as these materials exhibit remarkable variations in fundamental electrical, optical and magnetic properties that occur as one progresses from an “infinitely extended” solid to a particle of material consisting of a countable number of atoms.
An important class of nanostructured materials is block copolymers (BCPs). Some BCPs can spontaneously self-assemble to form nanoscale domains on a periodic lattice. (Bates, et al. Physics Today 1999, 52, 32; Leibler, Macromolecules 1980, 13, 1602; Bates, et al. Annual Reviews Physical Chemistry 1990, 41, 525.) For example, well ordered block copolymer thin films have been used as templates to pattern microelectronic devices and magnetic storage media, as sacrificial templates for the fabrication of inorganic mesostructured materials and for the preparation of polymeric nanoporous materials. (Park, et al. Science 1997, 276, 1401; Stoykovich, et al. Materials Today 2006, 9, 20; Harrison, et al. Journal of Vacuum Science & Technology B 1998, 16, 544; Jung, et al. Nano Letters 2008, 8, 3776; Cheng, et al. Advanced Materials 2001, 13, 1174; Park, et al., Science 2009, 323, 1030; Nagarajan, et al. Advanced Materials 2008, 20, 246; Pai, et al. Science 2004, 303, 507; Tirumala, et al. Chemistry of Materials 2007, 19, 5868; Hillmyer, in Block Copolymers Ii, Vol. 190, Springer-Verlag Berlin, Berlin 2005, 137; Kang, et al. Macromolecules 2009, 42, 455.) BCPs have also been used to direct the organization of hybrid materials, including polymer-nanoparticle composites. (Misner, et al. Advanced Materials 2003, 15, 221; Sohn, et al. Acta Polym. 1996, 47, 340.)
These materials have generated significant interest due to their potential in emerging areas such as photovoltaics and photonics. (Barber, et al. Organic Electronics 2006, 7, 508; Barran, et al. Macromolecules 2008, 41, 2701; Yang, et al. J. Mater. Chem. 2009, 19, 5416; Fink, et al. “Block copolymers as photonic bandgap materials”, presented at Workshop on Electromagnetic Crystal Structures, Laguna Beach, Calif., Jan. 4-6, 1999; Urbas, et al. Advanced Materials 2000, 12, 812; Urbas, et al. Macromolecules 1999, 32, 4748.). A recent review describes the governing thermodynamic challenges for realizing well ordered polymer-nanoparticle hybrids. Among the technological challenges for implementing block copolymer directed assembly are the need to achieve well ordered systems at high additive loadings and the need to maintain acceptable costs. (Balazs, et al. Science 2006, 314, 1107.)
One approach to ordered hybrid materials begins with a strongly segregated block copolymer template. In the absence of kinetic limitations, the phase segregation of A-B and A-B-A diblock and triblock copolymers is thermodynamically governed by the product χN where χ is the Flory-Huggins interaction parameter between the two dissimilar blocks and N is the total number of repeat units in all the blocks of the block copolymer. Upon segregation, the morphology is governed primarily by the relative volume fraction of the two blocks although the segregation strength of microphase segregated systems also plays a role near the phase boundaries. When segregation strength is high, A-B and A-B-A type block copolymers typically form spherical, cylindrical and lamellar morphologies as determined by their volume fractions. At lower segregation strengths in narrow ranges of volume fraction, bicontinuous gyroid morphologies can be observed. The phase segregation of A-B-A type triblock copolymers requires higher segregation strength (greater than about 18) as compared to diblock copolymer (greater than about 10.5). (Matsen, et al. Journal of Chemical Physics 1999, 111, 7139; Mayes, et al. Journal of Chemical Physics 1989, 91, 7228.)
Many applications would benefit from small domain sizes and, in the case of hybrid materials, high additive loadings. One challenge for achieving small domain sizes is that decreases in molar mass required to decrease the inter-domain spacing also weaken the segregation strength. It is often more desirable to increase the interaction parameter to maintain strong segregation. For hybrid materials, it is often desirable to maintain strong phase segregation and order upon the selective addition of additives to one domain of microphase segregated block copolymer templates. The amount of additives including nanoparticles that can be incorporated into BCPs is mostly limited to a few percent as higher loading of additives can disrupt the ordered BCP structure due to entropic penalties associated with polymer chain stretching required to accommodate the additives. (Balazs, et al. Science 2006, 314, 1107; Zhao, et al. Journal of Chemical Physics 2009, 130.) In other cases, either entropic considerations or lack of sufficient enthalpic interaction of the additives with the incorporating block have been associated with non-uniform distribution of particles within one phase. In addition, lack of sufficient interaction between the additive and the polymer chain can cause the additives to aggregate, which can lead to the loss of BCP order.
Novel, versatile additives effective in inducing and increasing order and nanostructures in polymeric materials and surfactants are strongly desired, particularly those that have unique physical and chemical attributes, as well as amendable to efficient and cost-effective production and application in various industries.